After surgery today.
She'd lost her appetite and was excessively thirsty. The vet examined her abdomen and performed an ultrasound and detected an abnormality on Tuesday and we had to take her back today for further investigations.
They found a tumour in her spleen, the size of a grapefruit. She was very lucky that her spleen hasn't hemmoraged. They took her to theatre and removed the tumour and her spleen. The human eye didn't spot any further abnormalities- not sure whether this means there's a chance it isn't malignant.
She's lost a lot of blood and is still sedated and lying on a heat mat. She's 13 and they are worried she will go into shock.
I'm feeling so terribly sad and worried. They said she was very anxious and pale when left, and I'd hate her to think we'd left her there. 
The vet said he'd never treated such a lovely natured dog .
Anyone have any experience or know what we can expect next? They'll call overnight if she passes, otherwise we have to call at 10am.